1. Field of the Invention
This invention relates to an electrical connector, and in particular to a decoupled BNC connector having an integral decoupling unit.
2. Description of Related Art
A BNC connector is a coaxial cable connector having an inner signal carrying conductor and an outer conductor surrounding the inner conductor which is ultimately connected to the shield of a cable, which is ideally at ground potential. Because shielded cables prevent RF frequency emissions from the cable, BNC configurations are often used for high frequency communications, such as in local area network (LAN) systems. Distinguishing features of the BNC connector include its bayonet coupling, for ease of interconnection, and a small profile, which is critical in LAN applications due to the small size and component densities of the circuit boards which carry LAN interfaces.
Originally, BNC connectors were mounted on a panel extending from the interface board, and the outer contact was directly connected to the panel by engagement between the panel and the outer contact, which formed the profile of the connector. However, a problem with direct grounding is that currents tend to be present in the cable shield due to external fields and differences in potential between ends of the cable. The former currents are known as transients and the latter currents are known as "ground loops". A solution to this problem which involved fitting the capacitor filter within the profile of the connector was first proposed in Amphenol's U.S. Pat. No. 4,772,221 (Kozlof). The Kozlof design enabled decoupling of the connector outer contact from the panel ground while at the same time permitting transients to pass. The present invention represents an improvement on the basic Kozlof design.
An example of a rear mount version of the Kozlof design as applied to a BNC connector having a cylindrical profile is shown in FIG. 1. The Kozlof BNC connector includes an inner contact 1 arranged to be connected to a trace on a circuit board through PCB tail 2, and to the inner conductor of a mating PCB connector through a cylindrical mating portion 3. The inner conductor is surrounded by an insulator member 4, which is secured with an outer conductor 5 having a ground tail 6 and a mating portion 7.
The Kozlof BNC connector is secured to a panel 8 by decoupling ring 9 and a nut 10 which is threaded onto threaded portion 11 of the connector. The decoupling ring includes a cylindrical dielectric having openings 12 in which are inserted chip capacitors 13. The capacitors are held in the housing 12 by washers 14 and 15, washer 15 including tines 16 which bias the capacitors against washer 14 and ensure a continuous electrical path between the panel and the outer conductor 5, the path including washer 15, capacitors 13, washer 14, another washer 17, a nut 10, and outer connector 5, washer 14 being essentially an extension of the outer contact. To ensure that outer contact 5 is not short-circuited to the panel, an insulator 18 is fitted between the panel 8 and around outer contact 5. The capacitors 13 are securely held in the decoupling ring, which at the same time facilitates assembly by permitting the decoupler ring to be fitted on the outer contact as a unit to form the connector profile.
Despite its advantages, however, the Kozlof connector has proved difficult to adapt to a second type of BNC connector which had a rectangular or parallelepiped-shaped dielectric outer housing rather than a cylindrical profile. The initial solution to the problem of decoupling a parallelepiped-shaped BNC connector, described in a published 1987 sales brochure by NTT corporation, and embodied in a connector sold at the time, was to place the chip capacitors directly within a recess in the outer dielectric body rather than in a discrete decoupling member, and to effect electrical connection to the panel by a panel engaging washer fitted over the capacitor recess. A conductive resilient member was placed between the capacitor and the outer conductor to ensure contact between the capacitor, the outer conductor, and the washer. Another decoupled parallelepiped shaped BNC connector was proposed in U.S. Pat. No. 4,884,982 to Fleming et al., shown in FIGS. 2(b) and 2(c). In this connector the capacitors are held in place by a resilient member which clipped the capacitors against the outer contact of the connector from the outside.
Both the NTT and Fleming designs have in common the use of an essentially externally mounted structure a hold s chip capacitor in a recess against a contact, utilizing a concept similar to that proposed several years earlier in U.S. Pat. No. 4,500,159 to Briones. In the Briones design, shown in FIG. 2(a), the chip capacitors 20 are fitted within openings 21 of a dielectric body 22 and biased against the contact 23 by means of a clip 24 supported by the outer conductive housing 25 of the connector. The present invention, in contrast, seeks to adapt the principle of using decoupling chip capacitors to a rectangular or parallelepiped shaped BNC connector by using the more integrated design of Kozlof in order to provide a structure which is easier to assemble and of greater mechanical stability than the prior designs.